1. Field of the Invention
This invention relates to sensors for detecting termite activity. This invention further relates to a method of detecting termite activity.
2. Description of the Related Art
Over the last four decades, control of subterranean termites has heavily relied on the use of liquid insecticides. Typically 100-200 gallons (or 5-10 kg active ingredient) of insecticide are applied to soil surrounding or beneath a house to exclude soil borne termites from structures. Because a subterranean termite colony can contain several hundred thousand to millions of termites that forage up to 300 feet from the nest, the majority of termites in a colony usually survive such soil treatments. In recent years, with less persistent insecticides being used as chemical barriers, re-infestation of surviving termites has become more frequent.
One alternative to conventional soil treatment is the use of slow-acting bait to control populations of subterranean termites. The monitoring/baiting program incorporating an insect growth regulator, hexaflumuron, as described by Su, N.-Y., Field Evaluation of a Hexaflumuron Bait for Population Suppression of Subterranean Termites (Isoptera: Rhinotermitidae), Journal of Economic Entomology 87: 389-397 (1994), is now commercially marketed as the Sentricon(copyright) Termite Colony Elimination System. To date there are numerous research data that demonstrate the elimination of colonies of various species of subterranean termites by the Sentricon system in the United States, Japan, Australia and Europe. Unlike conventional soil insecticide treatment, the monitoring/baiting program relies on routine monitoring to protect a given area. When termites are found in the monitoring stations, the monitoring devices are replaced with baits containing hexaflumuron. Baits containing the active ingredient are not used until termites are detected. This arrangement drastically reduces pesticide use for control of subterranean termites. It usually takes less than 1 gram of hexaflumuron to eliminate a colony of subterranean termites. Due to its low environmental impact, hexaflumuron is the first compound to be registered under the EPA""s Reduced Risk Pesticide Initiative.
One of the key components of the Sentricon system is the monitoring step. U.S. Pat. No. 5,329,726 (Thorne et al., Jul. 19, 1994) also adopted a xe2x80x9cdiagnosticxe2x80x9d phase before bait placement. However, this manual on-site monitoring is also the most labor intensive and costly element of the system.
There are other techniques available to detect the presence of termites in wood or soil. For example, Japanese Pat. No. 9-121742 (Sharp K.K., 5/1997) discloses an apparatus in which an optical sensor is employed to detect termite movement in a pre-drilled foraging tunnel in a wood block. However, the presence of subterranean termites is usually associated with elevated moisture (Su and Scheffrahn 1991, IRG/WP/1504). U.S. Pat. Nos. 4,812,741 (Stowell et al., Mar. 14, 1989) and 5,126,679 (Spry, Jun. 30, 1992) teach the use of a moisture sensor to signal the presence of termites. Further, termites are known to produce gases such as CO2 and methane. Such gases can be detected in the ground by use of subterranean probes (U.S. Pat. No. 3,943,750; McLaughlin et al., Mar. 16, 1976). Unfortunately, many other factors can produce moisture or subterranean gases, such as leaky plumbing, rainfall, putrefaction or fungal decay. Because these conditions are not unique to termite activity, monitoring stations adapted with these sensors or probes can cause false alarms and account for frequent, costly, and unnecessary on-site inspections.
Methods and devices for detecting infestation of termites have recently emerged. For instance, U.S. Pat. No. 5,592,774 (Galyon, Jan. 14, 1997) discloses a two-sensor system in which both sensors detect termite-presence conditions such as high humidity and gases. It is expected that when termites invade only one sensor, its condition (high moisture, gases, etc.) would be significantly different from the other, thus signaling the presence of termites. There is no guarantee, however, that only one sensor is invaded by termites, especially in areas of high termite population. Therefore, this arrangement does not address the problem of both sensors being simultaneously invaded by termites, thereby signaling a false negative response. In addition, microenvironment differences (slight humidity difference due to water flow in soil, etc.) can signal a false positive response with this type of system. Moreover, the presence of other soil dwelling insects such as earthworms, ants, and beetle larvae also produce termite-presence conditions such as high humidity and gases. Again, because such conditions are not unique to termite activity, invasion by these soil dwelling insects will cause false positives and costly, unnecessary on-site inspections.
Another method of termite monitoring focuses on detecting termite feeding by vibrations or sound transmitted through wood when termites tear and break wood fibers (U.S. Pat. No. 4,941,356, Pallaske 7/1990; Japanese Pat. H-7142827, Ikari 6/1995; PCT Publication No. WO93/23998). Such acoustic signals, however, can also be generated by other wood destroying insects such as powder beetles, bark beetles, house boarder, and carpenter ants, which also break wood fibers and thus can cause false positive responses. Moreover, these methods and apparatuses typically employ elaborate sensors that detect a narrow range of sound or vibration frequency, costly amplifiers to enhance the signals, and complex computer chips to interpret the signals.
These acoustic emission devices can be useful as hand-held tools to detect activities of termites and other wood destroying insects in structures (Scheffrahn et al. 1997, J. Econ. Entomol. 90: 492-502). Because 30-40 monitoring stations are needed to protect a house for a monitoring/baiting program, however, it is cost-inhibitory to utilize such acoustic emission devices (generally  greater than $1,000 per unit) in all of the stations. It is therefore highly desirable to incorporate a facile, inexpensive and specific termite-detecting sensor within the modern monitoring/baiting programs.
For example, PCT Publication No. WO 93/23998 (Dec. 9, 1993) discloses a simple efficient sensor that utilizes a thin strip of conductive soft metal (i.e. aluminum foil) placed over wooden blocks or stakes. It is proposed in this application that termites feeding on the wooden blocks break the soft metal circuit that is detectable by the lack of electric conductivity. Japanese Pat. No. 9-98701 (Ikari Shodoku K.K., Apr. 15, 1997) describes a termite-detecting device comprising an electrically conductive circuit secured on a medium damageable by termite feeding, such as paper.
A problem with using material such as wood, paper or other materials containing exclusively cellulose as the feeding medium, however, is that both false positive and false negative responses are common when sensors utilizing these materials are placed in the soil for an extended period of time. Outdoor elements such as rainfall, temperature fluctuation, and high humidity and biotic factors such as fungal decay and activity from other insects can trigger false positive responses. In fact, sensors incorporating wood or paper material produce false positive responses when conductive circuits are broken by expansion of cellulose-containing materials due to high humidity, rainfall or temperature fluctuation. Fungal decay and other insect activity such as tunneling by beetles or carpenter ants in wood also cause the circuit to break. Moreover, wet wood or paper can allow conductivity even when the circuit is broken by termites, thus causing a false negative response. It is for these reasons that sensors or termite-detecting devices that incorporate wood or paper, while arguably effective for a short term under field conditions, may not be ideally employed in a continuing monitoring program.
Therefore, a sensor used in a long-term continuous monitoring program for subterranean termites should desirably be specific to termite activity (true positive response). Furthermore, it should desirably not be susceptible to false positive responses caused by other environmental or biotic factors, i.e. the circuit should remain intact for an extended period (for example, months or years) absent the presence of termite activity.
Other detection apparatuses such as those taught in U.S. Pat. No. 3,564,750 (Burgess, Feb. 23, 1971), WO 93/23998 (Dec. 9, 1993) and Japanese Pat. No. 9-98701 (Ikari Shodoku K.K., Apr. 15, 1997) typically address the need for the true positive response, i.e. to be able to detect termite feeding, but do not address the issue of false negative responses.
This invention relates to a dimensionally stable (DS) sensor for use in a continuing monitoring program to detect termite activity.
Specifically, the present invention discloses a sensor that is specific to termite activity and not to the activity of other soil dwelling or wood destroying insects. The sensor is also dimensionally stable enough to be unaffected by environmental factors such as rainfall, high humidity, and temperature fluctuation, and by biotic factors such as fungal decay, which is typically associated with wood and other cellulose-containing materials.
The DS sensor comprises a dimensionally stable monitoring substrate. The monitoring substrate comprises a polymeric termite edible material that is resistant to dimensional expansion or contraction caused by meteorological elements such as changes in ambient humidity and/or temperature. Further, an electrically conductive circuit material is affixed to or embedded in one side of the monitoring substrate. The electrically conductive circuit material is breakable by termite activity, such as termite feeding or termite tunneling, and forms a continuous electrical bridging circuit such that when termite feeding breaks the electrically conductive circuit material, the continuous electrical bridging circuit is broken. The continuous electrical bridging circuit is also resistant to breakage for an extended period of time from exposure to meteorological elements such as changes in ambient humidity and/or temperature fluctuation. Thus, the dimensionally stable sensor is less susceptible to false positive responses and/or false negative responses in monitoring termite activity.
Alternatively, the sensor comprises a casing that houses the termite edible monitoring substrate. The casing itself is termite edible and serves to substantially isolate the substrate from the environment such that the monitoring substrate is effectively rendered dimensionally stable. The electrically conductive circuit material, in turn, is affixed to or embedded in the monitoring substrate.
The present invention also incorporates a tactile stimuli (TS) in the sensor to induce termite tunneling at desired locations and or directions, since termites tend to initiate tunneling or feeding in subtrates at any point of departure from smooth continuous surfaces that allow termite mandibles to grasp. By placing these TS at certain positions of a sensor in relation to the conductive circuits, timing of circuit breakage by termites can be regulated.
The present invention also teaches a method for continually monitoring termite activity in a particular site by utilizing at least one DS sensor and a detector for detecting breakage of the circuit due to termite feeding. The method provides for a more reliable way to specifically detect termite activity from other environmental and biotic factors, thus making it less susceptibe to false positive and false negative responses than other termite-detecting systems.